1. Field of the Invention
The invention relates to a payment system having electronic payment means, such as so-called "chip cards" or "smart cards". More specifically, the invention relates to a payment system including electronic payment means and one or more payment stations. Which payment stations are designed to receive, during a payment transaction, a monetary value by crediting, in the payment station, a first balance with a first value. Moreover of the payment means, is debited a second balance by a second value corresponding to the first value. Both balances represent numbers of calculation units.
2. Discussion of the Background
Electronic payment systems having (electronic) payment means, are known in practice. Prior art payment means (payment cards) comprise one or more integrated circuits ("chips"), which are mounted on a plastic substrate. In such an arrangement, at least one integrated circuit includes a processing unit (microprocessor) for carryingout operations, (e.g., computations and (cryptographic operations, and a storage unit (memory) for storing data, (e.g., monetary values and cryptographic data). Monetary values may be recorded as counter readings, with a certain counter reading corresponding to a certain amount of money in the currency in question. In the event of application of such payment means in a payment transaction, the monetary value is debited by lowering counter readings (possibly the contents of specific memory positions).
Since the possible applications of such payment means may be considerably extended if they are capable of being used in more than one country, it has been proposed to accommodate several currencies in one payment means. For this purpose, the storage means are provided with several counters, each of which updates a value of a certain currency. At the same time, the payment means is designed to each time draw on that currency, which is used in the country in question. Thus, this prior art payment means will have a counter which records a value in guilders (stock or "pot" of Dutch guilders) and another counter which records, e.g., a value in German marks. In this manner, it is possible to pay in the Netherlands with guilders and in Germany with marks.
Although a payment system having such prior art payment means is fit for use, it has several drawbacks. Thus, the number of different currencies is limited by the number of counters on the card which, due to the available memory space (or capacity of the hardware) is bound by a maximum. If such a payment means has been in use for some time in a relatively large number of countries, many counters will be in use and in practice be occupied by a small amount of foreign currency. This situation is similar to the one of ready cash, with a traveller, after his trip, in most cases being left with several coins of various currencies. As a result, it is not possible to add a new currency to the payment means without erasing a counter. In addition, such residual values together may constitute an expense for the user.
Prior art devices dealing with multiple currencies do not solve these problems. European patent application EP 0 251 619, for example, discloses a transaction card capable of performing payments in alternate currencies. A transaction limit may be converted into another currency, but the actual payments are made in a single currency, thus leaving the card holder with unspent amount in various currencies.
International patent application WO93/08545 discloses a value transfer system having a plurality of electronic purses. Different currencies may be loaded in the purses, and an amount held in a purse may be converted to a different currency. However, this conversion involves the floats of the respective currencies and cannot be handled by the card alone. This prior art payment system is thus not completely flexible with respect to different currencies.